The basic phenomena of a piezoelectric crystal is well known. If the crystal is struck, or exposed to a sudden shock, the crystal will generate electrical potential of relatively high voltage. This phenomena has been applied in industry as, for example, a voltage test device disclosed in U.S. Pat. No. 3,425,049 to Robinson. Other means for testing lamp circuits have been disclosed in U.S. Pat. No. 3,760,266 to Ocasio and U.S. Pat. No. 1,190,308 to Levy. The use of piezoelectric crystals has been applied to non-incandescent light sources such as gas filled discharge tubes as disclosed in U.S. Pat. No. 3,808,418 to Conrad, U.S. Pat. No. 4,523,261 to West and U.S. Pat. No. 4,748,361 to Taylor. However, the art has not recognized or fully appreciated the advantages of the Piezoelectric crystal and its applications for testing incandescent light bulbs.